An automatic transmission for a vehicle is designed to attain a plurality of speeds (gear ratios) by use of a planetary gear set(s) and the like, in order to convert output rotational speed and torque of an engine into appropriate level for a running state of the vehicle. Recently, the number of speeds (gear ratios) is increasing for the purpose of improving fuel economy. Because a gear ratio of first-speed is determined by a starting performance and an uphill performance of the vehicle, the number of speeds (gear ratios) tends to be increased in a high-speed side.
As a multispeed automatic transmission, a technique of the following Patent Literature 1 is known. The Patent Literature 1 discloses an automatic transmission including four planetary gear sets, two brakes and three clutches. This automatic transmission attains eight forward speeds and one reverse speed.